#define  _CRT_SECURE_NO_WARNINGS 1

#include <stdio.h>

int main()
{
	int a = 1;
	float sum = 0;
	while (a < 101)
	{
		if (a % 2 == 0)
			sum = sum - 1.0 / a;
		else
			sum = sum + 1.0 / a;
		a++;
	}
	printf("%f\n",sum);
	return 0;
}



